The United States is frantically trying to salvage a Syrian opposition conference that John Kerry plans to attend this week during his first official trip as U.S. secretary of state.

A senior Obama administration official said Sunday that Kerry has sent his top Syrian envoy to Cairo in hopes of convincing opposition leaders that their participation in the conference in Rome is critical to addressing questions from potential donors and securing additional aid from the United States and Europe.

Some members of the sharply divided Syrian Opposition Council are threatening to boycott Wednesday's meeting, which is the centerpiece of Kerry's nine-nation tour of Europe and the Middle East.

According to the official, U.S. envoy Robert Ford will say that the conference is a chance for foes of Syrian President Bashar Assad to make their case for new and enhanced aid - and get to know America's new chief diplomat, who has said he wants to propose new ideas to pressure Assad into leaving power.

The official spoke on condition of anonymity.

Kerry is on a self-described "listening tour" of Europe and the Mideast, focused on ending the crisis in Syria.

The former Democratic senator from Massachusetts has said he wants to discuss fresh proposals to ratchet up the pressure on Assad and make way for a democratic transition. Violence in Syria has killed at least 70,000 people.

Kerry has not elaborated on those plans, but there is internal debate in the Obama administration about stepping up aid to the rebels, perhaps to include lethal military assistance.